Heart burn (pyrosis), sysphoria after meal, flatulent feeling have been considered to be mainly caused by hyperacidity or hyperchylia. Recently, however, it is reported that similar symptoms are appeared in case of hypoacidity or anacidity. Patients in hypoacidity or anacidity may frequently take a general gastrointestinal or gastroenteric drug or an antacid, on concluding only by subjective symptoms or signs. In such a case, however, the symptoms may rather take the turn for the worse. Therefore, it is preferable to show no effect on patients in hypoacidity and in anacidity, and to give effects only on patients in hyperacidity or hyperchylia. With regard to antacids suitable for such objects, for example, Japanese Patent Application Laid-Open No. 101520/1975 (JP-A-50-101520) discloses a method of coating an antacid ingredient with a coating composition which dissolves at pH 5-6 or less, and Japanese Patent Application Laid-open No. 210012/1984 (JP-A-59-210012) discloses an antacid coated with a coating composition which is soluble only in acidic region.
In these antacids, however, polymers used as the coating compositions, for instance, polyvinylacetal diethylaminoacetate [AEA (trade name), manufactured by Sankyo, Co., Ltd., Japan] and a dimethylaminoethylmethacrylate-methacrylate copolymer [Eudragit E (trade name), manufactured by Rohm Pharma GmbH, Germany] are expensive. Further, an organic solvent (for example, alcohols, acetone, methylene chloride and the like) employed for coating with the coating composition causes some problems such as safety and remaining of the organic solvent.